This invention relates to a thermosetting epoxy resin composition having excellent mold release properties, flowability, and reliability in high temperature storage, which exhibits, once cured, high light resistance with reduced thermal discoloration, and in particular, reduced yellowing as well as high reliability. This invention also relates to a semiconductor device having a light-emitting element, light-receiving element, or other semiconductor element encapsulated with the cured product of such thermosetting epoxy resin composition.
With the decrease in the thickness and size as well as increase in the power of the semiconductor and electronic devices, severer requirements are imposed on the reliability of the materials used for encapsulating the semiconductor and electronic devices. For example, LED, LD (laser diode), and other semiconductor devices are used for various indicators and light sources because of their small size, brilliant light color, no burning out (due to the nature of the semiconductor device), superior operational properties, and resistance to repeated on/off operations.
Polyphthalamide (PPA) resins are widely used as a material for photocouplers and other semiconductor and electronic devices employing semiconductor elements.
However, with the dramatic progress in the optical semiconductor technology, optical semiconductor devices now use higher power and shorter wavelength, and encapsulation materials and cases currently used for the photocouplers and other optical semiconductor devices which are capable of emitting or receiving a high energy beam are no longer sufficient. More specifically, the encapsulation materials and cases for the semiconductor element using a conventional PPA resin as a non-colored or white material are likely to suffer from problems such as significant deterioration in the prolonged use, uneven discoloration, peeling, and decrease in the mechanical strength, and there is a demand for efficiently solving such problems.
More specifically, Japanese Patent No. 2656336 discloses an optical semiconductor device wherein the encapsulation is accomplished by curing a B-stage optical semiconductor-encapsulating epoxy resin composition comprising an epoxy resin, a curing agent, and a curing accelerator which are uniformly mixed at the molecular level. In this case, the epoxy resin mainly comprises a bisphenol A epoxy resin or a bisphenol F epoxy resin, and use of triglycidyl isocyanate is also mentioned. The triglycidyl isocyanate, however, is used in its Examples by adding a small amount to a bisphenol epoxy resin, and in the investigation by the present inventors, the B stage semiconductor encapsulating epoxy resin composition suffers from the problem of yellowing in long term storage at a high temperature.
Use of a triazine derivative epoxy resin in the epoxy resin composition for encapsulating a light-emitting element is mentioned in JP-A 2000-196151, JP-A 2003-224305, and JP-A 2005-306952. These publications, however, are not the cases where a B-stage epoxy resin is prepared by using triazine derivative epoxy resin with an acid anhydride.
Known publications which may be relevant with the present invention include those as mentioned above, and also, Japanese Patent No. 3512732, JP-A 2001-234032 and JP-A 2002-302533, and Electronics Packaging Technology, April 2004.